A. ACIS T_GAIN Epoch 56

The periodic ACIS T_GAIN correction upgrade for November 2013 through
January 2014 (Epoch 56) has
been released. The corrections are at nominal/expected levels of less
than 2% of the energy value. This upgrade as usual affects
observation data taken over the two most recent T_GAIN Epochs (56 and 55), and so
would update PHAs for OBS_IDs taken since 01 Aug 2013. Users with such datasets are
encouraged to revalidate their analysis results after reprocessing
their data with the upgraded CalDB files. For specific details of the
new calibrations in this release, see the technical details section below.

PIPELINES/TOOLS AFFECTED:

THREADS AFFECTED:

B. ACIS Secondary BADPIX File FP_TEMP Boundary Correction

Location:

$CALDB/data/chandra/acis/badpix/

Filename:

acisD2000-11-28badpix_secN0003.fits

An error has been found in the headers of the ACIS BADPIX file designated
for OBS_MODE=SECONDARY cases. These are "engineering runs" (ERs) and not ordinary
observations (ORs), primarily used to monitor the ACIS CTI effect and correct for
time-dependent gain drift. The error does not affect Standard Processing at all,
however it does affect manual reprocessing of archival ERs with very warm temperatures.
The fix is simply to expand the boundary on the focal plane temperature (FP_TEMP), which
is keyword "CBD10001" to be equal to "(148.15:188.15)K" for all headers in the above-named
file.

Reemphasizing, normal observations are not affected by this change in any way.

The existing HRC-I background (BKGRND) event lists version N0001 are now being
upgraded to version N0002. The newer version includes four additional files to cover the
years 2010, 2011, 2012, and 2013. All of the N0002 file have been compiled using the latest
level 1 calibration data, including the SAMP-based gains (GMAPs) and the latest DEGAP
corrections. We also find that there is significant improvement in background estimates of
more recent HRC-I observations with the newer applicable datasets. For further details, see
the technical details section below.

D. HRC-I/S RMF EBOUNDS Header Corrections

An errant keyword (TLMIN4) in the EBOUNDS extension headers of all of the HRC-I/S RMF files,
which has existed since their original releases, has been found to cause difficulties when using
CIAO 4.5 and later Datamodel commands such as dmcopy. The fix is simply
to delete the keyword from those EBOUNDS headers. It was necessary to use the FTOOL "fv" to remove
the keyword from each of the above files. Once removed, the DM problem ceases to occur.

The error causes a sporadic SegV and memory dump when using dmcopy with "opt=all" on any of the above
RMF files. While a fix to the software to prevent this problem has been ordered, a fix to the CalDB files is
reasonable, because the TLMIN4 keyword is not needed in EBOUNDS, which is a three-column table in all
cases.

The hypercube 2D PSF Library files had been used by the deprecated tool mkpsf to estimate the
shape of the PSF for off-axis source positions, primarily by interpolating between the numerous stored on-
and off-axis PSFs in the libraries. Mkpsf has been removed from CIAO distributions since CIAO 4.5 was released
in December 2012. At that point, it was posted on the CXC CALDB main page that the files would be dropped
from the CalDB after one more year of inclusion. That time has now expired.

Nominally the 2d_psf files above in the directories specified above may be (carfully!) deleted from the
CalDB once version 4.6.1 or later is installed on your local system. Use of the old mkpsf tool with
any earlier release of CIAO or CalDB is strongly discouraged, in favor of the much more reliable and accurate
online Chandra raytrace application ChaRT. In the event
that the 2d_psf files are lost and simply must be made available, they may be requested from the Chandra
Helpdesk. Keep in mind that they will no longer be indexed in CalDB, and can't be selected automatically by
mkpsf, but must be pset manually instead.

PIPELINES/TOOLS AFFECTED:

None.

THREADS AFFECTED:

None.

III. TECHNICAL DETAILS

A. ACIS T_GAIN Epoch 56

The ACIS time-dependent gain corrections (T_GAIN) have recently
been updated for current changes from the previous T_GAIN epoch,
specifically Epoch 56, which was November 2013 through January 2014.
With the addition of these new corrections, derived from ACIS External
Cal Source (ECS) data taken during radiation zone passes, the CalDB
files extending from August-October 2013 (i.e. Epoch 55) have been
finalized, and new non-interpolating T_GAIN files are now implemented
for Epoch 56.

The magnitudes (in eV) of the new gain corrections, versus photon energy,
are given in Figs. 1-3 below. The corrections are of the usual order in
magnitude, specifically less than 2.0% of the photon energy value. Fig. 1
below gives the corrections for the ACIS-I aimpoint on chip ACIS-3, for the
CTI-corrected case, which is the only one applicable to FI chips. Fig. 2
gives the corrections for the ACIS-S aimpoint on ACIS-7, for the case
where the BI chips are CTI-corrected. Finally Fig. 3 gives the corrections
for ACIS-7 for NON-CTI-corrected BI chips. These would be relevant to GRADED
DATAMODE observations with ACIS-S, for example.

Long term trends for chips I3 and S3 are plotted below in Figure
4a and b, through Epoch 56, the latest release. The chip locations for these
plots are given in the respective labels above the plots. Note that
the locations are not the aimpoint positions, as with Figs. 1-3 above, but
are near the centers of each chip.

Figs 4a and 4b: Long term gain trends for specific
ECS line energies from Epoch 1 to Epoch 56 inclusive, and for the
positions on the respective chips given in the figure
labels. (Click on images to expand the plots.)

B. ACIS Secondary BADPIX File FP_TEMP Boundary Correction

The change to the FP_TEMP boundary condition applied to the SECONDARY mode BADPIX file
was necessary for those using CIAO to reprocess the L1 events files from the archive when
the FP_TEMP of the ER exceeds 164.15K (-109C). The problem does not appear in the standard
data processing of SECONDARY mode data, because the FP_TEMP is not determined in the
environment at the time acis_build_badpix is run in SDP. Hence, the FP_TEMP boundary condition
is ignored by the CalDB query interface in SDP.

An example of such an ER is 53549, which has an ACIS focal plan temperature of 164.762K. The
procedure regenerating the *bpix1.fits file in reprocessing may be seen in the thread Reprocessing Data to Create a New L2 Events File
under the "Running
acis_build_badpix" section. While this thread does not include the necessary information to
specify the eventual output L1 and L2 event lists, the section on bpix1 regeneration is fine
for this illustration.

Using CalDB versions 4.5.0 through 4.5.9, there will be a CalDB search error for the ACIS BADPIX file
for OBS_ID 53549 as follows:

The SECONDARY mode BADPIX file is selected, and the procedure may move forward.

C. HRC-I Background Event Lists Version 2

DEMONSTRATION OF THE NEW BKGRND FILES

A test of several of the HRC-I BKGRND files in fluxed image background subtraction is provided
in Fig. 5 below. In this test, two 2013 observations are combined, and compared with a background image
generated from three different HRC-I BKGRND files.

The procedure used was to combine OBS_IDs 14916 and 14917 the CIAO contributed script
merge_obs, then compute the background from three
comparable HRC-I BKGRND files, namely:

TEST 1: hrciD2013-01-01bkgrndN0002.fits, the new BKGRND file that is applicable to these data.

TEST 2: hrciD2009-01-01bkgrndN0001.fits, the previously released BKGRND that would have been
selected from CalDB.

TEST 3: hrciD2009-01-01bkgrndN0002.fits, the new version of the 2009 BKGRND file, for comparison.

All processing parameters were the same in all tests. The background-subtracted counts images are shown
in the figure, and the plots below are from the red projection regions in the corresponding frames
(sum of counts along the smaller of the projection rectangle's axes plotted vs. the other rectangle axis).

There is no discernible difference between the two 2009 background maps (TEST 2 and TEST 3),
but they both underestimate the actual background, which is to be expected since
they are from 4 years earlier and background is increasing with time. The 2013
background map (TEST 1) isn't perfect but does a much better job.

Fig. 5: Results of testing the background subtraction from two combined 2013 Obs_IDs
using (TEST 1) the new 2013 HRC-I BKGRND N0002 file, (TEST 2) the old 2009 BKGRND N0001
file, and (TEST 3) the new 2009 N0002 BKGRND file.

D. HRC-I/S RMF EBOUNDS Header Corrections

An example of the sporadic error message obtained when dmcopy is applied to the
HRC-I RMF file as might occur when manipulating the CalDB HRC RMF files in CIAO:

A software fix will be included in CIAO in the future to eliminate this
error. However, the problem with the RMFs is being fixed by removing the
errant TLMIN4 keyword in the EBOUNDS header of each of the HRC RMF files.

Matching CIAO and CALDB Versions

News

CalDB 4.6.7
an upgrade to CalDB 4.6.5 and later versions, has been released. Notable additions include
the ACIS T_GAIN Epoch 60 quarterly upgrades (Nov-Jan 2015), and a correction to the HRC index
file. See the CalDB 4.6.7
Release Notes for details.

16 Dec 2014

CalDB 4.6.5,
an upgrade to CalDB version 4.5.9 and later versions, has been released. Notable additions
included are ACIS T_GAIN Epoch 59 updates (Aug-Oct 2014), HRC-I GMAP and PIBGSPEC updates for 2014,
and HRC-S QE version N0013 and QEU (version N0007) modifications. See the
CalDB 4.6.5 Release
notes for details.

CalDB 4.6.3,
an upgrade to CalDB version 4.5.9 and later versions, has been released. Notable additions
included are ACIS T_GAIN Epoch 58 updates (May-July 2014), HRC-S QEU files for 2014-2020,
mitigation of the HRC-S QEU Caveats.
CalDB 4.6.3 Release
notes for details.

25 Jul 2014

HRC-S QEU File Search Error Caveat
added. This applies to all HRC-S observations taken in 1999 and in 2014. A workaround is
prescribed on this page. The fix will be released in mid August 2014. NOTE: These have been
mitigated with the CalDB 4.6.3 release on 29 Aug 2014!

09 Jul 2014

CalDB 4.6.2, an upgrade to CalDB version 4.5.9
and later versions, has been released. It contains (a) an ACIS quarterly T_GAIN
upgrade (Epoch 57, Feb-Apr 2014), (b) upgrades to PCAD CALALIGN files for 2003, 2006, 2012,
and 2013, and finally (c) an upgrade to the ACIS CONTAM file to improve on-axis calibration
performance from April 2013 onward. See the
CalDB 4.6.2 Release
notes for details.

09 Apr 2014

CalDB 4.6.1.1, a patch upgrade to CalDB 4.6.1
which corrects the HRC branch index listings of the latest two HRC-I background event lists
for 2012 and 2013, so that they are selected appropriately for OBS_IDs taken after
(UTC) 2012-01-01T00:00:00. See the
CalDB 4.6.1.1 Release
notes for details.

26 Mar 2014

CalDB 4.6.1, an upgrade to CalDB version 4.5.9
and later versions, has been released. It contains (a) an ACIS quarterly T_GAIN
upgrade (Epoch 56, Nov-Jan 2014), as well as (b) a new HRC-I BKGRND event list library
which adds new files for the four most recent calendar years (2010-2013). See the
CalDB 4.6.1 Release
notes for details.